1) noun. Stuff that is made up for the purpose of placating someone, or passing an exam, or getting elected to office. Most often false or ridiculous.
2) verb. To generate bullshit.
3) interjection. Accusing someone of bullshitting.
4) adjective. Identifying or suspecting something as bullshit.

In all usages, the term can be shortened to "bull" or "BS".

1) My essay was complete bullshit.
2) Man, I gotta learn to bullshit properly if I want to pass this English exam.
3) "I was sick all last week!" "Bullshit!"
4) That is such a bullshit answer.

1. An obvious lie
2. A game, in which at least 3 players, pref. 4 or more participate. Each player is dealt as close to the same amount of the deck as possible. The players then take turns laying one or more cards of the same rank down. The rank increases as the play goes around. For example, 4 players are playing. Player 1 lays down 2 Aces, player 2 lays down 3 twos, player 3 lays down 1 three. Player two, however, believes player 3 had no threes, and calls out "bullshit". Player 3, in fact, had not laid down a three, but a king. Player 3 must pick up the cards laid down thus far. Had player two been wrong, he would have had to pick those cards up. Player four then lays down 2 fours, and the play continues until every player but one is rid of their cards. The first out wins, second is second place, etc.